Electromagnetic indicator



B. M. GORDON ETAL 2,943,313 ELECTROMAGNETIC INDICATOR 3 Sheets-Sheet 1INVENTORS BERNARD M. GORDON HECTOR R. DUROCHER AMERICO SICO June 28,1960 Filed Feb. 25, 1957 FIG.4

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4 & if? I M will 5 1 F v 1 n H 1 w w m m a a B June 28, 1960 B. M.GORDON EIAL 2,943,313

ELECTROMAGNETIC INDICATOR Filed Feb. 25, 1957 3 $heets-$heet 2 INVENTORSBERNARD M. GO N HECTOR R. DUR ER AMERICO SICO A TZDRNE) n q (0 9 w l-LLl.

June 28, 1960 B. M. GORDON ETAL 2,943,313

ELECTROMAGNETIC INDICATOR Filed Feb. 25, 1957 5 Sheets-Sheet 3 FIG. 3

/ N VE N T0193 BERNARD M. GORDON HECTOR R. DUROCHER AMERICO SICO r97ATTORNEY United States Patent 2,943,313 ELECTROMAGNETIC INDICATORBernard M. Gordon, Newton, Mass., Hector R. Duroeher, Nashua, N.H., andAmerica Sico, Revere, Mass., assignors to Epsco, Incorporated, Boston,Mass, a corporatlon of Massachusetts Filed Feb. 25, 1957, Ser..No.641,932

13 Claims. (Cl. 340-378) The present invention relates in general -to anelectromagnetic data display system, and more particularly concernsnovel, compact and relatively low cost apparatus responsive to externalelectrical excitation for reliably indicating any one of a plurality ofpreselected characters or indicia.

Within the broad subject classification of data display devices,virtually innumerable mechanical, electromagnetic and electronictechniques have been described in the literature, and a comparativelylarge number of specific instrument types are commercially available atthe present time. Perhaps the most successful of the priorelectromagnetic character display units is dependent upon themultiposition stepping relay; which while quite satisfactory for suchapplications as stock quotation boards, is relatively costly, noisy,slow in operation and mechanically complex. Further, its weightprecludes use in airborne systems, and wear problems attendant pawl andrachet mechanisms severely limit the reliability which may beanticipated.

Recent innovations in electronic tubes have resulted in novel glow-tubedischarge indicators, an example being an elongated neon tube having aplurality of axially spaced filamentary cathodes, each having theconfiguration of the character to be displayed. These devices areeminently eifective in darkened surroundings andmay be operated at highspeed, but are subject to disadvantages such as complete inflexibilitywith respect to character selection and the poor reliability and highfailure expectancies of gas discharge tubes.

The present invention contemplates and has as a primary object theprovision of an electromagnetic data display device of novel, simplifieddesign and construction offering positive, unambiguous, high speedcharacter selection and presentation wholly without complex pawl andrachet linkages, electronic circuits and components, which isparticularly adaptable to low cost mass production techniques. Thisinvention represents an extension of the principles of the copendingapplication of Bernard M. Gordon and Randall L. Gibson, entitledIndicating Device, Serial No. 584,803, filed May 14, 1956.

Broadly speaking, the present invention utilizes a character bearingmember in association with an electromagnetic structure selectivelyenergizable to produce any one of a plurality of discrete magnetic fieldorientations. A magnetic device whose motion is controlled by theselected field controls the displacement of the character member, and aviewing window is provided for visual observation of the chosencharacter. In accordance with the principles of this invention, for eachinscribed figure to be displayed, two closely adjacent, magneticallydetermined stable positions are available for the character bearingmember, one fixed by the electromagnetic structure when electricalexcitation is applied thereto, and the other by an independent staticmagnetizable member which coacts with the magnetic device associatedwith the character bearing member in the absence of electricalexcitation. This permits precise, unambiguous centering of each of thecharacters to be displayed, provides a restraining torque whichprecludes drift of the character bearing member due to environmentaldisturbances such as vibration, and of special significance, yields amagnetic circuit without dead-spots or conditions of magneticequilibrium which would otherwise tend to prevent the development ofdisplacement forces upon the character member despite the appliedexcitation.

More specifically, in one aspect of the present invention, the dataindicating device comprises a stator having a symmetrical, circularconfiguration of electromagnets capable of establishing a discretenumber of magnetic field orientations in response to the selectiveapplication of current to the coils thereof. The characters to bedisplayed are inscribed upon the outer cylindrical surface of a lightweight, low inertia rotor which is activated by an attached salient polepermanent magnet whose angular orientation is initially controlled bythe stator field.

A symmetrical array of static magnetizable elements is fixed in thespace between the rotor permanent magnet and the stator, and arranged toprovide, by mutual magnetic attraction, a number of discreteorientations for the rotor magnet, equal to the number available fromthe stator electromagnets but slightly displaced therefrom. In otherwords, when the appropriate current is applied to the statorelectromagnets, the rotor magnet immediately assumes the angularorientation of the magnetic field thus established, which is completelyindependent of the presence of the static magnetizable elements. Uponthe interruption of this current, however, the attractive force betweenthe respective, slightly displaced static element and the rotor magnetcontrols, and the rotor is accordingly displaced angularly and lockedinto .a new position in proximity with the static element. By preciselypositioning the magnetizable elements, it is possible to fix with acorresponding degree of accuracy, the display position of each of thecharacters to be viewed through the window provided therefor.

As will become apparent as the discussion proceeds, numerous novelmechanical concepts are combined with the objective of achievingmanufacturing simplicity and cost reduction while enhancing flexibilityand utility. Thus, a simplified toroidal stator structure is used whicheliminates the tedious machining and assembly required for a salientpole design, and further permits incapsulation into a unitary, troublefree package. The housing is arranged so that a multiplicity of likeindicating units maybe joined together in an integral compact packageallowing numbers or codes of any order to be displayed. While be ing ofminimum inertia to permit rapid angular adjustment, the rotor isnevertheless arranged so that viscous fluid damping may be added toenhance its transient response to applied signals, and a single coverplate simultaneously affords both shielding from stray magnetic fieldsand magnetic damping.

Ease of final assembly is another object of this invention, and thesimplified assembly technique allows rapid initial adjustment to insureaccurate display. Adjustments once made will be retained for the life ofthe device.

Other objects and advantages will best be understood from the followingdetailed specification when read in connection with the accompanyingdrawing in which:

Fig. l is a fragmentary front view of a panel illustrating the manner inwhich an assembly of indicating units embodying this invention may bemounted to furnish a multidigit data display;

Fig. 2 is a perspective view of one of the data indicating unitsembodying the principles of this invention;

Fig. 3 is an axially exploded perspective view which illustrates the keycomponents of the data indicating unit illustrated in Fig. 2;

Fig. 4 is a top view, partly in cross-section, of an assembledindicating unit, the cross-sectional area being taken along a diameterof the device indicated in Fig. 2;

Fig. 5 is a schematic circuit diagram illustrating the electricalinterconnection of the electromagnets within the indicating device ofFig. 2 and the mode of actuation thereof;

Fig. 6A andFig. 6B are respectively end and front views of theindicating device and serve to illustrate the relative angularorientation of several of the components under a particular electricalcondition; and

Fig. 7A and Fig. 7B are respectively end and front views of theindicating device and illustrate the orientation of these components foran electrical condition other than that shown in Fig. 6.

Throughout the several views of the drawing, like reference numeralswill be used to designate like components. I

With reference now to the drawing and more particularly to Fig. 1thereof, there is shown a portion of a panel 11 formed with an elongatedrectangular opening 12 through which are visible the character displayportions of a mechanically cascaded group of identical indicator units13, each of which embodies the principles of this invention. As willbecome more apparent from the description which follows, any selectedindicia may be displayed by the respective indicating units 13 as afunction of applied electrical excitation. The indicia chosen will, ofcourse, be a function of the specific application; for example, assumingeach indicator as eapable of displaying all ten decimal digits, theapparatus disclosed in Fig. 1 may readily be used to furnish a visualoutput of a five decade electronic counter. On the other hand, it isunnecessary that the display be digital in character, and any or all ofthe devices may be employed to display alphabetic or special symbolsassociated with the apparatus into which the indicators areincorporated.

Figs. 2 to 7 inclusive disclose the specific mechanical and theelectrical details, including the mode of operation, of one of thedevices 13 shown in Fig. 1. By viritue of the fact that the bulk of theapplications for indicators having these general specifications relateto the presentation of the ten decimal digits, an indicator so designedhas been chosen for detailed illustration and discussion herein. It willbe understood, however, that by relatively simple design changes, theprinciples of this invention may be extended to indicators capable ofdisplaying greater or fewer digits, letters or symbols.

Fig. 2 is a perspective view which generally illustrates the externalphysical characteristics of the indicator of this invention. Allelectrical and mechanical elements of the device are completely enclosedwithin a thin cylindrical housing 14, formed with a single rectangularwindow 15, through which the digits inscribed upon the outer cylindricalsurface of a coaxial rotor 16, may be viewed.

A multiplicity of wires 18 extend out of the indicator for connection toan external circuit for electrical control of the digit presentation.

With the physical appearance of the indicating device 13 in view,reference is now made simultaneously to Figs. 3 and 4 which disclose themechanical details of each of the key components both individually andas assembled.

More specifically, housing 14 is seen to comprise a relatively shortcylinder closed at one end by a circular end wall. The edges of window15 may be beveled to emphasize the outline thereof and to generallyimprove its appearance in a display. An annular ridge 25 is formed ontheclosed end of housing 14 and is beveled at 26, as best illustrated inFig. 4, to provide a circular edge which will mate exactly with thecircular edge 27 of another of the indicating devices 13. In this mannerthe array shown in Fig. l, or any larger or smaller group of devices,may be built up as a rigid integrated structure. The inner edge of ridge25 confines a circular region which is adapted to receive a disc-shapedmagnetic end plate 31 having a central opening 32 and threesymmetrically positioned countersunk holes 33. A central opening 34 inthe side Wall of housing 14 is aligned axially with opening 32 and threearcuate slots 35 are aligned with openings 33. The thickness of endplate 31 corresponds exactly to the depth of the recess formed withincircular ridge 25; consequently, when the plate is appropriatelyinserted and the fiat-head screws 36 and 37 passed through therespective counter-sunk openings, a smooth external surface ispresented, as best illustrated in Fig. 4.

Returning to the details of housing 14, a slot 41 is provided in the endwall which extends to a small notch 42 in the cylindrical surfacethereof. As best illustrated in Fig. 4, this arrangement permitswithdrawal of the wires 18 without interference with the seating of endplate 31 in the recess provided by ridge 25.

Turning now to rotor 16, this component is seen. to comprise a centralhub 43 which diverges into an integral substantially circular side wall44 which in turn supports the thin integral character bearingcylindrical surface 17.

Returning momentarily to Fig. 2, it will be observed that the circularend wall of rotor 16 contains a plurality of relatively largeperforations 21 which advantageously function to minimize the inertia ofthe rotor and as a consequence enhance the speed of response to externalsignals.

A key 45 is fitted in mating keyways provided in hub 43 and in apermanent magnet 46, the latter having ogival or similar sharply pointedmagnetic poles. When assembled as shown in Fig. 4, magnet 46 and rotor16 rotate as a unit.

An arbor 51 rotatably supports rotor 16 within a cylindrical housing 14.As shown, arbor 51 is provided with a threaded axial opening 52 which onassembly is engaged by screw 36. Annular ridge 53 forms a seat to firmlyposition arbor 51 against the inner wall of housing 14. Cylindricalsurface 54 accepts ball bearing 55, which on assembly as shown in Fig.4, rotatably supports rotor 16 in housing 14. A saucer-shaped cover 56,secured in place by snap ring 57, keeps the rotating elements dust anddirt free.

An electrotmagnetic stator 61 is symmetrically and co axially disposedwithin housing 14 and the manner in which this component is constructedis best seen by simultaneous reference to Figs. 3, 4 and 6A. Themagnetic component of this assembly is a toroid 62 formed of a pluralityof stacked iron laminations. With particular reference to Fig. 6A, eachof the magnetic core laminations comprises a flat circular stamping ofmagnetic material which is formed with a relatively narrow slit 63. Inassembling the magnetic structure 61 the requisite number oflaminations, for example, five as shown in the drawing, are placed oneupon the other with the slits 63 in transverse alignment. At this pointthe laminations as a group are bent open, forming a helical core, andfor the decimal indicator under discussion, ten coil forms 64, eachwound with a respective solenoid type coil 65, are slipped on to themagnetic structure. As best shown in Fig. 6A, coil forms 64 are sodimensioned as to abut one another along the inner circular edge thereofwhen in position. This arrangement makes it unnecessary to use spacersor other means to assure a reasonably symmetrical distribution of coils65 about laminations 62.

With the coils in place, the laminar core structure is allowed to springback to its normal circular form, and to avoid an abrupt air gap, ascrewdri er or like implement is used to rotate each of the laminationswith reference to the others so that the respective slits 63 aresymmetrically distributed. For example, when using five laminations,each of the circular elements may be shifted approximately seventy-twodegrees with reference to the others. Under the circumstances the effectof the individual air gaps 63 is negligible. The number of turns in eachof the solenoidal coils 65 will be determined by design factors, such asapplied voltage, but for general application may consist of severalthousand turns of relatively fine wire.

Fig. is a schematic diagram illustrating the wiring symmetry of thecircular array of coils 65 about the mag netic core (not shown in thisfigure). Conventional dot notation has been used to indicate windingdirection and it is seen that the dotted end of each coil is joined tothe undotted end of the next adjacent coil. Insofar as the magneticfield is concerned, this is effectively the equivalent of Winding atapped, continuous toroidal winding upon core 62.

Wires 18 which are used for external actuation extend from the junctionsbetween each two adjacent coils. The wires interconnecting the adjacentcoils 65 are not shown in Fig. 6A but the group of output wires 18 hasbeen illustrated in both Figs. 4 and 6A. Evidently the number of outputwires 18 is exactly equal to the number of coils used upon the toroidalmagnetic core 62, and for a decimal display device this number of courseis ten.

With coils 65 appropriately disposed upon the magnetic core structure,and the output leads 18 suitably attached, the array of electromagnetsis inserted into a stamped or molded open toroidal shell 66 ofnon-magnetic material. Thereafter the coil structure is potted orencased in a plastic compound 67 which not only rigidly secures the coilstructure relative to shell 66, but permanently seals the electricalcomponents against moisture. During the incapsulation process, threesymmetrical threaded holes maybe formed in the region between coils,these being aligned properly for engagement by screws 37 to secure theelectromagnetic stator 61 to the inner surface of the end wall ofhousing 14.

A relatively thin non-magnetic cylinder 71 is positioned in the spacebetween magnet 46 and the inner surface of stator 61. This element, asis best illustrated in Figs. 3 and 6A, is formed with small rectangularslots 72 equal in number to the stator electromagnets 65, and according--ly equal in number to the digits to be displayed. Slots 72. As shown inFig. 6A the cross-section of these magnetizable elements is such thateach exactly fills the space provided therefor in the cylindrical member71.

Fig. '4 demonstrates the manner in which the components individuallypictured in Fig. 3 are assembled into an indicating unit of the typeillustrated in Fig. 2. The exact order of assembly is not too critical;typically however, circular end plate 31 may be placed in the recessprovided therefor, and stator 61 then secured by screws 37 (a loose fitpending final adjustment). Cylindrical member 71 is preferablypress-fitted or cemented to the inner surface of shell 66, and thiscomposite unit is rotatable about the inwardly facing circular ridge 75provided on the inner side wall of housing '14. The angular relationshipof the magnetic elements 73 and the coil assembly will be more fuilyconsidered below. The subassembly of arbor'51, ball bearing 55, dustcover 56, clamp ring 57, magnet 46 and rotor 16 are fastened in theposition shown by the single screw 36.

Returning now to Fig. 5, the manner in which the indicator unit isactuated will be discussed briefly. Each of the wires 18, which may becolor-coded for convenience current I which divides equally betweenopposite symmetrical semi-circles of the coils 65. The net elfect ofboth currents U2 is to establish a diametrical magnetic field designatedby the vector B.

Vector B is one of the ten possible discrete diametrical magnetic fieldswhich may be created by rotation of switch arms 79 and 80. Each of thesefields, which has the effect of displaying a respective digit, will beseparated from adjacent fields by the angular separation of adjacentcoils 65. For the decimal indicator this is thirty-six degrees, howeversome variation in this distribution may be expected because, as notedearlier, a high degree of precision was not a primary requirement inmounting coils 65 on the supporting core.

Although rotation of opposed switch arms 79 and 80 is effective inrotating vector B, it should be apparent that this is not the only meansby'which a desired field orientation may be established. For example, ifan indicator unit is used as a computer output device, all ten wires18'may be directly coupled to the computer, and energization of any twoopposite wires will set up a field and select a digit for display.

Reference is now made to Figs. 6A and 7A for illustration of therelative orientation of certain of the key components in the assembledindicator, and for a discussion of the significance and utility of themagnetic elements 73. Line 81 has been drawn for reference purposes fromthe center through a point midway between two adjacent coil forms 64.The purpose of this line is to define the position of one of the tendiscrete magnetic field vectors B, such as the one shown upon thecircuit diagram, Fig. 5.

Thus, these figures show that cylinder 71 is fixed within the stator andoriented within housing 14 so as to provide a substantially uniformangular separation, designated on the drawing as 0, between theindividual magnetic elements 73 and the respective mid-points betweenadjacent electromagnets.

With current flowing as in Fig. 5, and assuming that the device is inperfect adjustment, salient pole-magnet 46 will rapidly rotate and alignitself with the field vector B, Fig. 6A; the sharply defined N and Spoles falling along line 81. Assuming further, that with power thusapplied, the selected character is digit 5; the manner in which the 5appears in the viewing window is shown in Fig. 6B. Thus, note that the 5is off-centered by a small amount. If now the current I is cut off, themagnetic field designated by vector B disappears, with the result thatthe force of attraction between each of the salient poles of magnet 46and the immediately adjacent magnetic element 73 will cause angularrotation of the magnet, and the attached rotor, to the rest positionshown in Fig. 7A. Displacement through angle 0 will now bring digit 5into the symmetrical, centered position within window 15 shown in Fig.7B.

Thus, speaking generally, for each of the ten discrete orientations ofthe magnetic field vector B in the decimal device being considered,there exists a fixed, stable angular position for magnet 46. Inaddition, in the region of each of these ten discrete orientations,there exists a second stable position for magnet 46 which is defined, asin Fig. 7A, by the respective magnetic. element 73. Stated otherwise,when power is applied to a particular opposite set of input terminals,rotor 16 is brought to a first stableposition where it remains untilpower is cut off; immediately thereafter, the rotor is pulled throughthe slight angle 0 by magnetic forces to the second stable position.

The specific advantages of this magnetic configuration may be bestdemonstrated by an example. The excitationfshown in Fig. 5 was assumedto be that which would bring the character 5 into the viewing window.With the decimal digits to 9 uniformly marked upon the periphery ofcylindricalsurface 17, the digit 0 is brought into view by reversing thepolarity of current through the same input wires which brought digitinto view. If now the angular orientationshown in Fig. 6A were the restposition for viewing digit 5, reversal of field vector B would in factdevelop no rotational torque on magnet 46, other than that which mightbe generated due to inherent imperfections and inaccuracies inmanufacturing the device. Effectiv ly, for a situation which demanded a180 reversal or the rotor, a condition of unbalanced or unstableequilibrium would exist which would result either in no'inotionwhatsoever or exceedingly slow initial rotation due to the negligibletorque resulting from machining and alignment errors. I

on the other hand, Figs. 6A and 7A demonstrate that the application ofpower is used to efiiect an approximate alignment and that immediatelyafter power cut-off, a definite displacement from the original aligningfield is accomplished in reaching the correct position. Thereafter, thisdisplacement will permit the development of substantial rotationaltorque even if a digit 180 displaced from the digit under observation isselected by the external source. Y

Further advantages of the device are apparent from an examination ofFigs. 6A and 7B. Obviously precision angular separation of themultiplicity of electromagnets wound on core 64 would be difiicult, andperhaps an extraordinarily expensive task. If alignment of each of thedigits to be viewed within the viewing window 15 were to be dependentupon the establishment of ten magnetic field vectors each preciselythirty-six degrees apart, an exceptional degree of care in the windingand mounting of each of the coils would be required. As disclosed in thedrawing, however, the stator electromagnets serve primarily to positionthe rotor close to the rest position, while the exact determination ofthe position of the digit in the viewing window is made by the tenmagnetic elements 73 supported by cylinder 71. Obviously, it is arelatively simple task to space these magnetic elements thirty-sixdegrees apart, whereby each of the ten digits will be precisely centeredwithin the viewing window as illustrated in Fig. 7B.

Of interest however, is the fact that the magnetizable elements 73perform still another vital function, perhaps best illustrated withreference to Fig. 7A; namely, that of providing a restraining torquewhich tends to keep the rotor 16 in the selected positionnotwithstanding vibration, shock or other environmental interference. Itis especially significant to note that a minimum of spacing existsbetween the salient poles of magnet 46 and the inner surface of cylinder71. Thus a modest amount of torque would be required to displace magnet46 from the position shown in Fig. 7A unless power is applied to theinput wires of the device.

Previous discussio'n assumed precise initial adjustment of the indicatorto obtain the operating results discussed in connection with Figs. 6 and7. Referring to Figs. 3 and 6A, it may be seen that the angularrelationship specified for the assembly including the statorelectromagnets and the magnetizable elements 73 may be obtained duringassembly by angular adjustment of the entire stator structure 61relative to the housing 14 through the aid of the arcuate openings 35.When this relative magnetic orientation is accomplished, all four screws36 and 37 may be tightened, and further adjustment will not be required.

Magnet 46 has been described as having ogival shaped, salient poles, thelatter being formed either by molding or grinding. In the manufacture ofpermanent magnets it is not infrequent that the magnetic poles are notpre- 8 cisely apart. The effect of such inherent defect upon the'presentindicator is best demonstrated in Fig. 7A where point 87 is fordiscussion purposes assumed to represent the true magnetic pole.Although this is not precisely at the physical extremity of the magnet,the effect of this displacement will be negligible since the sharp taperplaces the displaced magnetic pole sufliciently inward radially from thepointed end, that the latter will, in fact, be determinative of angularposition when at rest as shown in Fig. 7A.

Disc 31, as disclosed earlier, performs the dual function of shieldingthe interior of the display unit from stray magnetic fields and offeringa degree of magnetic damping to rotation of magnet 46. While treatingthe subject of damping, it should be observed that it is also possible,if desired, to add a degree of viscous damping through the use of afluid in ball bearing 55. For this purpose it is preferably that acustomary ball retainer type hearing (not shown) he used. The fluidwhich may be of silicone base, and retained by capillary action issufiicicnt to provide the necessary transient damping. The region 91shown in the assembly Fig. 4 may, through capillary action, also be usedto retain a modest amount of damping fluid if desired. The closeproximity of rotor and arbor surfaces will preclude fluid leakageirrespective of mounting position of the indicator.

Special note should be taken of the nature of the electrical signalrequired to achieve the results illustrated in Figs. 6 and 7. When poweris applied for the purpose of changing digits the torque developed uponrotor 16 by field vector B causes rapid acceleration to the newposition. Obviously, if the power is cut off before this new position isreached, the rotor will spin free, and though it will ultimately come torest due to the attraction of some magnetic element 73, there remains ahigh probability of an erroneous reading. It is therefore necessary toapply power for a sufficient time to insure a correct orientation ofrotor 16. It is, in fact, desirable to utilize some safety factor in thecurrent pulse to preclude erroneous reading if for any reason themechanism should behave in a sluggish manner.

Although the preceding discussion has assumed that the power is turnedoff shortly after the rotor arrives at the position defined by themagnetic field, it is possible to utilize the device shown underconditions in which the power is on throughout the display period of achar-' acter. Under such operating conditions, adjustment would be madeso that the characters were symmetrically disposed in the viewing window15 during periods of energrzatiou. The static magnetizable elements 73would still function to create an unbalanced torque condition in theevent that a selected digit fell diametrically opposite the onepreviously indicated. The advantage of operating the device with thepower on throughout the period of character display of course is thatthe residual or retaining torque is much higher than that achieved underthe conditions previously described in connection with Fig. 7A. On theother hand the disadvantage is larger power consumption and a dependenceupon power even if a particular reading were to be retained for anextensive period of time.

Certain comments are now in order concerning the choice of materials forfabrication of the device. For the purpose of minimizing weight,particularly for airborne applications, it is highly desirable that bothhousing 14 and rotor 16 be made of dimensionally stable plastics, whichmay either be machined or die molded to the configuration showndepending upon the economics of the situation. Cylinder 71 may be eithermolded or extruded of plastic, but may also be made of a non-magneticmetal such as aluminum.

The size of the device, of course, may be scaled to meet ounces havebeen successfully operated as high speed decimal indicators for theoutput of computing machinery. The maximum time required to achieve adigit change w'as'0.6 second, and speedier response was achieved byincreasing input power.

Of course, many modifications of this device may now become apparent tothose skilled in the art. Consequently, the spirit and scope of thisinvention should not be considered as defined by the foregoingdisclosure, but by the appended claims.

What is claimed is:

1. Indicating apparatus for displaying a predetermined plurality ofdiscrete indicia associated with a rotatable magnet comprising,electrically energizable means for selectively providing a magneticfield in the region of said magnet having one of a like plurality ofdiscrete orientations angularly separated about a common center, and acorresponding plurality of static magnetic elements disposed about saidmagnet respectively associated with and angularly offset relative toeach said discrete orientation, whereby in each of said orientations twostable and distinctive display positions are provided for the respectiveone of said indicia, one of said display positions being determined bysaid rotatable magnet and said electrically generated magnetic fieldsubstantially independently of said static magnetic elements, the otherbeing determined solely by said rotatable magnet and said staticmagnetic elements in the absence of electrical energization.

2. Indicating apparatus as in claim 1 wherein said electricallyenergizable means comprises a substantially circular configuration ofelectromagnets and wherein said static magnetic elements comprise acorresponding configuration of sharply-defined magnetizable members.

3. A character indicating device comprising a character bearing member,a configuration of electromagnets selectively energizable to furnish anyone of a plurality of discrete magnetic field orientations, a likeconfiguration of sharply-defined static magnetizable elements, and amagnet having a pair of sharply-defined diametrically opposite polesassociated with said character bearing member and coacting with saidstatic magnetizable elements whereby the orientation of said characterbearing member is controlled exclusively by said static elements in theabsence of electrical energization of said electromagnets.

4. A character indicating device comprising a character bearing member,a configuration of electromagnets selectively energizable to furnish anyone of a plurality of discrete magnetic field orientations angularlyseparated about a common center, a like configuration of sharply-definedstatic magnetizable elements, each of said elements being angularlyofiset from a respective magnetic field orientation, and a magneticmember having sharply-defined diametrically opposite poles associatedwith said character bearing element and arranged for angular movementunder control of the discrete magnetic field selectively established byenergization of said electromagnets and for angular movement exclusivelyunder control of the respective magnetizable element in the absence ofenergization of said electromagnets.

5. A character indicating device comprising, a generally cylindricalhousing, a circular array of electromagnets forming a stator disposedwithin and affixed to said housing, arotor including a hub forsupporting a salient pole magnet rotatable within said array ofelectromagnets and a character bearing member aflixed to and extendingoutwardly of said hub and having a cylindrical surface rotatable in theregion between said electromagnets and said housing, a circular array ofsharply-defined magnetic elements equal in number to said electromagnetsdisposed in the region between said salient pole magnet and saidelectromagnets, and a window in said cylindrical housing for displayinga portion of said character bearing member.

6. A character indicating device comprising, a housing having agenerally hollow cylindrical portion terminated by at least one circularend wall, an arbor extending into said cylindrical portion andsubstantially centrally aifixed to said end wall, a stator structureformed of a plurality of electrically energizable coils symmetricallyand concentrically distributed about said arbor and afiixed to the innersurface of said end wall, a rotor structure including a hub rotatablysupported upon said arbor, said rotor structure further including acircular portion extending ities of said salient pole magnet, and awindow in said cylindrical portion of said housing for displaying anarea of the outer surface of said cylindrical character bearing portionof said rotor structure.

7. A character indicating device comprising, a housing having agenerally hollow cylindrical portion terminated by at least one circularend wall, an arbor extending into said cylindrical portion andsubstantially centrally atfixed to said end wall, a stator structureincluding a substantially circular magnetic core bearing a plurality ofsymmetrically distributed coils thereon, said stator structure beingconcentrically affixed to the inner surface of said circular end walland arranged for angular adjustment about said arbor, the ends of eachof said coils being electrically connected to the ends of the coilsimmediately adjacent thereto, lead wires extending from each of saidcoil connections through an aperture in said housing, a rotor structureincluding a hub rotatably supported upon said arbor, said rotorstructure further including a circular portion extending radiallyoutward of said hub opposite said end wall and terminating in agenerally cylindrical reentrant character bearing portion rotatable inthe region between said stator structure and the inner surface of saidcylindrical portion of said housing, a salient pole permanent magnetrigidly secured to said hub and rotatable therewith within the circularregion defined by said coils, sharply-defined staticv magnetic elementsequal in number to said coils and symmetrically distributed about andaflixed to said stator structure in the region between said coils andthe extremities of said salient pole magnet, and a window in saidcylindrical portion of said housing for displaying an area of the outersurface of said cylindrical character bearing portion of said rotorstructure.

8. A character indicating device comprising, a housing having agenerally hollow cylindrical portion terminated by at least one circularend wall, an arbor extending into said cylindrical portion andsubstantially centrally afiixed to said end wall, a stator structureincluding a substantially circular magnetic core bearing a plurality ofsymmetrically distributed coils thereon, said stator structure beingconcentrically aflixed to the inner surface of said circular end walland arranged for angular adjustment about said arbor, the ends of eachof said coils being electrically connected to the ends of the coilsimmediately adjacent thereto, lead wires extending from each of saidcoil connections through an aperture in said housing, a rotor structureincluding a hub rotatably supported upon said arbor, said rotorstructure further including a circular portion extending radiallyoutward of said hub opposite said end wall and terminating in agenerally cylindrical reentrant character bearing portion rotatable inthe region between said stator structure and the inner surface of saidcylindrical portion of said housing, a permanent magnet having a pair ofdiametrically opposed ogival shaped salient poles and a central openingadapted to fit over said hub, said magnet being rigidly aflixed to saidrotor structure and rotatable therewith within the circular regiondefined by said coils, a cylindrical member for symmetrically supportingmagnetic elements equal in number to said coils, said cylindrical memberbeing afiixed to said stator structure in the region between said coilsand the pointed extremities of said salient poles, and a window in saidcylindrical portion of said housing for displaying an area of the outersurface of said cylindrical character bearing portion of said rotorstructure.

9. Character indicating apparatus asin claim 8 wherein the inner surfaceof said circular end wall of said housing is formed with an inwardlyfacing circular ridge rotatably supporting said magnetic elementsupporting cylinder and said stator structure affixed thereto.

10. Character indicating apparatus as in claim 6 where in the outersurface of said circular end wall of said housing is formed with acircular recess, and a circular plate of magnetic material equal indimensions and secured within said recess for magnetically shieldingsaid apparatus and magnetically damping rotation of said permanentmagnet affixed to said rotor structure.

11. Character indicating apparatus as in claim 10 wherein said hub andsaid arbor confine a region having a capillary clearance to permitrotation therebetween and adapted to enclose a viscous damping fluidsubstantially without leakage.

12. Character indicating apparatus as in claim 8 wherein said magneticelements are angularly oliset about the axis of said arbor in relationto the angularly separated discrete magnetic fields generated byelectrically energizing diametrically opposite coil connections, wherebymotion of said permanent magnet and rotor structure is controlled by themagnetic field generated by said coils when energized and by saidmagnetic elements when deenergized.

13. Character indicating apparatus as in claim 12 and including indiciainscribed on said outer surface of said character bearing portion ofsaid rotor, said indicia being arranged thereon to be centrally disposedin said viewing window in said housing when the angular position of saidrotor structure is fixed by interaction of said permanent magnet and therespective magnetic elements in the absence of energization of saidcoils.

References Cited in the file of this patent UNITED STATES PATENTS594,979 Barrett Dec. 7, 1897 1,058,545 Caldwell Apr. 8, 1913 2,649,559Wargo Aug. 18, 1953 FOREIGN PATENTS 137,255 Great Britain Jan. 8, 1920

